Injection-moulding tool for the production of information carriers in disc form

ABSTRACT

An injection-molding tool ( 10 ) for the production of information carriers in disc form, in particular in the form of CDs and/or DVDs, comprises for the forming of an injection mold ( 25 ) a first and a second mirror block ( 11  and  12,  respectively), which lie opposite each other and are movable in relation to each other for opening and closing the mold and also a form ring ( 20 ), which concentrically encloses the first mirror block ( 11 ) and closes off the injection mold ( 25 ) towards the outer edge and is movable in relation to the first mirror block ( 11 ), means for reducing the friction when there is a movement of the form ring ( 20 ) in relation to the first mirror block ( 11 ) being provided between the first mirror block ( 11 ) and the form ring ( 20 ) enclosing it.  
     In the case of such an injection mold, the production of information-carrier discs of a particularly high quality is made possible in a simple way by the means comprising a sliding ring ( 21; 21   a,b,c ) arranged concentrically between the first mirror block ( 11 ) and the form ring ( 20 ) enclosing it.

TECHNICAL FIELD

[0001] The present invention relates to the field of injection-molding technology. It concerns an injection-molding tool for the production of information carriers in disc form according to the precharacterizing clause of claim 1.

[0002] Such an injection-molding tool is known, for example, from the printed document WO-A1-99/37471.

PRIOR ART

[0003] For producing optically readable information carriers such as audio CDs, CD-ROMs, video CDs or DVDs, injection-molding tools which form an injection mold by means of two (cylindrical) mirror blocks lying opposite each other and movable in relation to each other are used. On one of the two mirror blocks there is usually releasably fastened a thin, disc-shaped stamper, which stamps the tracks containing the information during the injection molding of the information carrier being formed. At the outer edge, the injection mold is often bounded by a form ring, which concentrically surrounds one of the mirror blocks.

[0004] The form ring projects beyond the planar molding surface of the mirror block enclosed by it and is displaceable in relation to this mirror block in the axial direction. If the injection mold is closed by an axial movement of the two mirror blocks towards each other, the form ring comes to rest on the opposite mirror block on account of the projection and closes the mold, while the mirror block concentrically enclosed by it is at a predetermined distance from the opposite mirror block. The hot plastic is then infected under high pressure into the disc-shaped cavity formed in this way. Once the cavity of the injection mold has been filled, the mirror block enclosed by the form ring is moved a little towards the other mirror block—in order to achieve a high quality of the information carrier—, while the form ring remains fixed in place (see in this respect FIGS. 2 and 3 of WO-A1-99/37471, cited at the beginning).

[0005] However, the relative movement taking place in this phase of the production process between the mirror block and the form ring enclosing it gives rise to problems for the following reasons: in order that the form ring can slide freely over the mirror block during the relative movement, a certain fit is necessary. If this fit is too large, plastic can get into the gap during injection and forms undesired flash on the molded information carrier disc. If, on the other hand, the fit is too close, excessive friction values may occur, in particular if the mirror block and form ring are at different temperatures, hindering the relative movement and—because both parts are generally made of steel—possibly leading to seizing or jamming of the form ring on the mirror block.

[0006] In order to ensure a low sliding friction between the mirror block and the form ring when there is a relatively close fit, it has already been proposed in WO-A1-99/37471, cited at the beginning, to provide the surfaces sliding on one another of the mirror block and the form ring with a special coating which reduces the friction. However, it is disadvantageous in this case that the coating of the parts entails high expenditure, and that the coating generally influences the heat removal from the injection mold.

[0007] In EP-A1-0 899 075, to ensure a good relative mobility between a mirror block and a ring concentrically enclosing the mirror block, a linear ball bearing (75 in FIG. 5) is provided between the two parts. However, in this case the ring is not a form ring, which forms part of the injection mold, but a guide ring, which assists the centering of the two mirror blocks with respect to each other.

[0008] Finally, U.S. Pat. No. 5,018,962 discloses an injection-molding tool, comprising two mirror blocks and a form ring, for the production of CDs, in which a concentric retaining ring (15 in FIG. 1) for the stamper resting on one of the mirror blocks is provided between the form ring and the said mirror block. During opening and closing, the form ring slides over both mirror blocks. However, special precautions for reducing the friction during these sliding processes are not taken.

SUMMARY OF THE INVENTION

[0009] It is therefore the object of the invention to provide an injection-molding tool for the production of information carriers in disc form which avoids the disadvantages of known injection-molding tools and is distinguished in particular by simplified production, can be used unproblematically and flexibly and makes possible the production of information carrier discs of a particularly high quality.

[0010] The object is achieved by the features of claim 1 altogether. The essence of the invention is to provide between the parts sliding over one another of the injection-molding tool, to be specific the first mirror block and the form ring enclosing it, a special sliding ring which prevents direct friction between the mirror block and the form ring. Since the sliding ring is a separate component, if need be it can easily be exchanged or replaced, without having to change the other parts of the injection-molding tool; in a corresponding way, a free choice of the material of the sliding ring allows the sliding properties to be optimized. Since the sliding ring inevitably forms part of the injection mold at the edge, the form of the injection-molded part can be influenced by suitable shaping and selection. Finally, it is possible by a specific choice of the material of the sliding ring, to improve the heat removal in the edge region of the injection mold.

[0011] A first preferred embodiment of the injection-molding tool according to the invention is distinguished in that the sliding ring consists of a material reducing the sliding friction, in particular of copper, a copper alloy such as bronze or else a plastics material such as Teflon. As a result, equally good sliding properties and good thermal conductivities can be realized in the edge region of the injection mold. The sliding ring can also be provided with a friction-reducing coating, for example a PVD coating (PVD=physical vapour deposit).

[0012] Influencing the form of the injection-molded part by corresponding shaping of the sliding ring according to the invention can be achieved in various ways: if the first mirror block bounds the injection mold with an essentially planar surface, and the sliding ring adjoins the planar surface of the first mirror block with its end face facing the injection mold in such a way that it is flush with it, and enlarges it towards the outside, an injection-molded part with a planar underside up to the outer edge is obtained.

[0013] If, on the other hand, the sliding ring has a bevel on its end face facing the injection mold in such a way that the information carrier produced in the injection mold has a chamfer at its outer edge, the injection-molded part is correspondingly provided with a chamfer.

[0014] If, finally, the sliding ring has a peripheral depression on its end face facing the injection mold in such a way that the information carrier produced in the injection mold has an elevated, annular scratch guard at its outer edge, the injection-molded part is correspondingly provided with a scratch guard in the form of an annular bead.

[0015] Further embodiments emerge from the dependent claims

BRIEF EXPLANATION OF THE FIGURES

[0016] The invention is to be explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing, in which:

[0017]FIG. 1 shows in a longitudinal section a preferred exemplary embodiment of an injection-molding tool according to the invention in a simplified representation;

[0018]FIG. 2 shows a first exemplary embodiment of a sliding ring according to the invention with a flush-adjoining end face (FIG. 2c) and the edge regions of a resultant finished CD (FIG. 2a) or DVD (FIG. 2b);

[0019]FIG. 3 shows a second exemplary embodiment of a sliding ring according to the invention with a bevelled end face (FIG. 3c) and the edge regions of a resultant finished CD (FIG. 3a) or DVD (FIG. 3b); and

[0020]FIG. 4 shows a third exemplary embodiment of a sliding ring according to the invention with a peripheral depression in the end face (FIG. 4c) and the edge regions of a resultant finished CD (FIG. 4a) or DVD (FIG. 4b).

WAYS OF CARRYING OUT THE INVENTION

[0021] In FIG. 1, a preferred exemplary embodiment of an injection-molding tool according to the invention is reproduced in a longitudinal section. The figure is in this case simplified to the extent that the necessary screw fittings, springs, seals and operator-control elements have not been represented. The injection-molding tool 10, shown in the closed state, comprises a central component, a first (left) mirror block 11, a second (right) mirror block 12 and a form ring (venting ring) 20 concentrically enclosing the first mirror block 11, which together form the injection mold 25. The mirror blocks 11, 12 are in each case fitted into a centering ring 13 and 14, respectively, concentrically surrounding them. The information is stamped into the injection-molded part (the CD) during the injection molding by means of a stamper 19, which, as a thin disc, bears against the molding surface of the second mirror block 12 and is held in the center by a bushing-shaped stamper holder 18. For the connection of the injection-molding tool 10 to the nozzle of the injection-molding machine (not represented), a screw bush 17 reaching through the center of the second mirror block 12 into the injection mold 25 and opening conically outwards is provided.

[0022] Arranged opposite the sprue bush 17, lying concentrically in one another and (indicated by the double-headed arrows) movable in relation to one another, are an ejector sleeve 16, a punch 15 and a sprue ejector 23. With the sprue ejector 23, the sprue 22 remaining in the inner bore of the sprue bush 17 can be ejected. With the punch 15, the central opening in the injection-molded CD is punched out. With the ejector sleeve 16, finally, the finished CD can be ejected after the injection mold 25 has been opened.

[0023] The form ring 20 is displaceably mounted in the centering ring 13 and is pressed by springs (not represented) in the direction of the second mirror block 12. It can be withdrawn by means of a pneumatically driven actuating element 24. According to the invention, the form ring 20 does not bear with its inner side directly against the outer side of the first mirror block 11 but is separated from the latter by a sliding ring 21, which rests concentrically on the outer side of the first mirror block 11 in an offset provided for this purpose. The sliding ring 21 essentially has the form of a hollow cylinder and preferably consists of copper, a copper alloy such as bronze or else a plastics material such as Teflon. It consequently forms for the form ring 20, consisting of steel, and the first mirror block 11, consisting of steel, a sliding bearing with good thermal conduction, which ensures improved heat removal in the edge region of the injection mold 25 and consequently ensures improved optical and electrical values in the outer region of the CD. On account of the good sliding properties, a relatively close fit can be chosen between the sliding ring 21 and the first mirror block 11, so that the formation of flash between the mirror block 11 and form ring 20 is significantly reduced.

[0024] In addition to the advantages already set out with regard to the quality which can be achieved, the introduction of the sliding ring 21 makes possible an additional degree of freedom in the shaping of the injection-molded CD, because one of the end faces of the sliding ring is part of the injection mold. This advantage can be explained with reference to FIGS. 2 to 4, the Subfigures (c) in each case showing the cross-sectional form of the sliding ring used, and the Subfigures (a) and (b) in each case showing the resultant edge forms for a CD (Subfigure a) and for a DVD composed of two part-discs (Subfigure b).

[0025] In the case of FIG. 2, the end face of the sliding ring 21 a facing the injection mold 25 is planar and adjoins the first mirror block 11 in such a way that it is flush with it. The underside of the finished CD 30 (FIG. 2a) and the upper side and underside of the finished DVD 31 (FIG. 2b) are correspondingly formed in such a way that they are planar up to the outer edge.

[0026] In the case of FIG. 3, the end face of the sliding ring 21 b facing the injection mold 25 is configured as a bevel 26. The underside of the finished CD 30 (FIG. 3a) and the upper side and underside of the finished DVD 31 (FIG. 3b) are correspondingly provided with a chamfer 27 at the outer edge.

[0027] In the case of FIG. 4, finally, the end face of the sliding ring 21 c facing the injection mold 25 is formed as a peripheral depression 28. The underside of the finished CD 30 (FIG. 4a) and the upper side and underside of the finished DVD 31 (FIG. 4b) are correspondingly provided at the outer edge with a scratch guard 29 in the form of an annular bead.

[0028] It goes without saying that other forms can also be produced in the edge region of the finished CD or DVD by different forms of shaping for the sliding ring 21.

[0029] Altogether, the invention provides an injection-molding tool for the production of information carriers in disc form (CDs, DVDs etc.) which is distinguished by the following properties and advantages:

[0030] improved sliding properties between mirror block and form ring;

[0031] greater functional window when there is a varying temperature difference between mirror block and form ring;

[0032] improvement in optical quality on the substrate of the information carrier, specifically in the outer region;

[0033] improved cooling properties on the outside and, as a result, better optical and electrical values in the outer region of the information carrier;

[0034] new geometries possible (chamfering, scratch guard etc.);

[0035] reduction in the formation of flash between mirror block and form ring.

LIST OF DESIGNATIONS

[0036]10 injection-molding tool

[0037]11,12 mirror block

[0038]13,14 centering ring

[0039]15 punch

[0040]16 ejector sleeve

[0041]17 sprue bush

[0042]18 stamper holder

[0043]19 stamper

[0044]20 form or venting ring

[0045]21,21 a,b,c sliding ring

[0046]22 sprue

[0047]23 sprue ejector

[0048]24 actuating element (form ring)

[0049]25 injection mold (cavity)

[0050]26 bevel

[0051]27 chamfer

[0052]28 depression (peripheral)

[0053]29 scratch guard

[0054]30 CD

[0055]31 DVD 

1. Injection-molding tool (10) for the production of information carriers in disc form, in particular in the form of CDs (30) and/or DVDs (31), which injection-molding tool (10) comprises for the forming of an injection mold (25) a first and a second mirror block (11 and 12, respectively), which lie opposite each other and are movable in relation to each other for opening and closing the mold, and also a form ring (20), which concentrically encloses the first mirror block (11) and closes off the injection mold (25) towards the outer edge and is movable in relation to the first mirror block (11), means for reducing the friction when there is a movement of the form ring (20) in relation to the first mirror block (11) being provided between the first mirror block (11) and the form ring (20) enclosing it, characterized in that the means comprise a sliding ring (21; 21 a,b,c) arranged concentrically between the first mirror block (11) and the form ring (20) enclosing it.
 2. Injection-molding tool according to claim 1, characterized in that the sliding ring (21; 21 a,b,c) consists of a material reducing the sliding friction.
 3. Injection-molding tool according to claim 2, characterized in that the sliding ring (21; 21 a,b,c) consists of copper, a copper alloy such as bronze or else a plastics material such as Teflon.
 4. Injection-molding tool according to one of claims 1 to 3, characterized in that the first mirror block (11) bounds the injection mold (25) with an essentially planar surface, and in that the sliding ring (21 a) adjoins the planar surface of the first mirror block (11) with its end face facing the injection mold (25) in such a way that it is flush with it, and enlarges it towards the outside.
 5. Injection-molding tool according to one of claims 1 to 3, characterized in that the first mirror block (11) bounds the injection mold (25) with an essentially planar surface, and in that the sliding ring (21 b) has a bevel (26) on its end face facing the injection mold (25) in such a way that the information carrier (30, 31) produced in the injection mold (25) has a chamfer (37) at its outer edge.
 6. Injection-molding tool according to one of claims 1 to 3, characterized in that the first mirror block (11) bounds the injection mold (35) with an essentially planar surface, and in that the sliding ring (21 c) has a peripheral depression (28) on its end face facing the injection mold (25) in such a way that the information carrier (30, 31) produced in the injection mold (25) has an elevated, annular scratch guard (29) at its outer edge.
 7. Injection-molding tool according to one of claims 1 to 6, characterized in that the sliding ring (21; 21 a,b,c) rests on the first mirror block (11).
 8. Injection-molding tool according to one of the claims 1 to 7, characterized in that the sliding ring (21; 21 a,b,c) is provided with a friction-reducing coating. 